Methylation of toluene to para-xylene catalyzed by crystalline silica

ABSTRACT

An improved catalytic process for making para-xylene from toluene and a methylating agent employing the described crystalline silica as catalyst, said catalyst optionally promoted by one or more compounds of arsenic, phosphorus, magnesium, boron, antimony and amorphous silica. Preferred promoters are boron compounds, antimony compounds, and amorphous silica.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns the reaction of toluene and a methylating agentin the presence of a crystalline silica catalyst, with or withoutpromoters, to produce para-xylene.

2. Description of the Prior Art

Aluminosilicate zeolites are known as catalysts for the methylation oftoluene. U.S. Pat. No. 3,965,208, U.S. Pat. No. 4,100,215, U.S. Pat. No.4,127,616, and Yashima et al, "Alkylation On Synthetic Zeolites",Journal of Catalysis, 16, 273 and 280 (1970), are representative of theart which describes zeolites as catalysts for toluene methylation.

It is known from OS No. 2,755,770 that all or part of the alumina in analuminosilicate zeolite can be replaced by iron oxide or by iron oxidein combination with gallium oxide. The OS states that the describedmetallosilicates are useful as catalysts in the methylation of toluene.The OS, therefore, broadens the store of knowledge concerning zeolitesuseful in methylation of toluene by suggesting the utility ofiron-containing metallosilicates.

The interrelationship of the alumina (or alumina substitute) and silicacontent of zeolites relevant to their utility in the toluene methylationprocess has apparently not been studied. However, U.S. Pat. No.3,894,103 explores the silica/alumina ratio relevant to the use ofzeolites as catalysts in converting lower aliphatic alcohols such asmethanol to aromatic compounds. From the Table bridging columns 5 and 6of U.S. Pat. No. 3,894,103 it is clear that the amount of aromaticproduct produced decreases as the silica/alumina ratio is increased. Ata ratio of 35/1 the amount of aromatic product produced is 77% or 79%;see columns 1 and 2 of the Table. At a ratio of 1300/1 no aromaticproduct is produced; see column 10 of the Table. The data presented inthis patent would lead one to conclude that high ratios of silica toalumina are generally detrimental to catalytic activity. Thus, one wouldnot expect very much activity of crystalline silica in the catalysis ofa toluene methylation reaction.

Several crystalline silica compositions, both with and withoutpromoters, are known. See, for instance: U.S. Pat. No. 3,941,871, U.S.Pat. No. 4,061,724, U.S. Pat. No. 4,073,865, U.S. Pat. No. 4,104,294,and Flanigen et al, "Silicalite, A New Hydrophobic Crystalline SilicaMolecular Sieve", Nature, Vol. 271, 9 February 1978, pages 512 to 516.

Only in U.S. Pat. No. 4,104,294, however, is there any intimation thatcrystalline silica compositions might be useful as catalysts. Thestatement that such compositions are suitable for use in "hydrocarbonconversion" reactions is nonspecific, unexplained, and unsupported.Therefore, the patent does little to propel one skilled in the art touse crystalline silica as a catalyst since the weight of authority isthat such a material would, at best, be a poor catalyst. The statementconcerning the extensive area of "hydrocarbon conversion" does nothingto teach the art that such catalysts would have utility in toluenemethylation or, in fact, in any specific transformation process.

Against the background of the prior art as described heretofore, it hasnow been found that crystalline silica containing substantially noalumina or alumina-substitute in the crystal lattice is an excellentcatalyst for the specific process of methylating toluene to producexylene, which process is characterized by particularly high proportionsof the para isomer.

SUMMARY OF THE INVENTION

This invention concerns an improved process for producing para-xylene bythe catalytic methylation of toluene. The improvement resides primarilyin the use of crystalline silica compositions, with or withoutpromoters, as the catalysts. Contemplated promoters include arsenicoxide, phosphorus oxide, magnesium oxide, boron oxide, antimony oxide,amorphous silica, and mixtures thereof, said promoter(s) being presentin an amount from 0 to about 50%, preferably 0.3% to 25%, based on totalweight of metal oxide in the catalyst. Preferred promoters are boronoxide, antimony oxide and amorphous silica. The most preferred promoteris amorphous silica.

The mole ratio of toluene to methylating agent in the reactant feed canvary between about 1 to 50/1 respectively. Preferred ratios are 3 to20/1 and the most preferred ratios are 5 to 15/1. Reactant ratios richerin methylating agent than about 1 part per part of toluene may lead tothe formation of undesirable by-products. Reactant ratios richer intoluene than about 50 parts per part of methylating agent may lead tohigh energy costs to separate the para-xylene and recycle the reactants.

The rate of reactant feed, in terms of weight hourly space velocity,WHSV, is the weight of reactant feed per weight of catalyst per hour.WHSV may vary between about 1 to 500. Preferably, reactant feeds willvary between 2 to 250 and most preferably between 3 to 100.

The crystalline silica employed in the process of this invention ismicroporous; it has an average pore size of about 6 Å diameter and alattice network comprising substantially only silica. Although thecrystalline silica may contain small amounts of alumina, iron orgermanium impurities adsorbed or occluded therein, such materials do notform part of the lattice network. Therefore, the crystalline silicaemployed in the process of this invention cannot be considered ametallosilicate.

The crystalline silica in its activated form after calcination at 550°C. in air for 4 hours has a mean refractive index of 1.419±0.01. Thespecific gravity of the crystalline silica activated by calcining in thesame way, at 550° C. in air for 4 hours, is 1.93±0.05 gm/cc as measuredby water displacement. This high specific gravity is believed to beindicative of good catalyst stability.

The crystalline silica catalyst, after heating in air at 550° C. for atleast about 2 hours displays a characteristic X-ray powder diffractionpattern having its six strongest lines at interplanar d spacings (Å) andrelative intensities (I/I_(o)) substantially as set out in Table A.

                  TABLE A                                                         ______________________________________                                                Å                                                                              I/I.sub.o                                                        ______________________________________                                                3.85 100                                                                      11.11                                                                              87                                                                       10.02                                                                              60                                                                       3.81 57                                                                       9.93 51                                                                       3.71 49                                                               ______________________________________                                    

These X-ray data were obtained by standard techniques employing K-alphadoublet of copper radiation and a scintillation counter spectrometerwith a strip chart pen recorder. Peak heights, I, and positions as afunction of 2 times theta, where theta is the Bragg angle, weremeasured. From these values, relative intensities and interplanar dspacings were calculated.

Typical methylating agents include methanol, dimethylether,methylchloride, methylbromide and dimethylsulfide. One skilled in theart will know what other methylating agents may be employed in theprocess of this invention based on the description provided herein.Preferred methylating agents are methanol and dimethylether. Methanol ismost preferred.

The process of this invention is characterized by high yields of xylenebased on toluene and methylating agent, as well as surprisingly highspecificity to para-xylene at the expense of the ortho and meta isomers.

Of the xylene isomers, i.e., ortho-, meta- and para-xylene, the latteris of particular value being useful in the manufacture of terephthalicacid which is an intermediate in the manufacture of synthetic fibersincluding those bearing the Dacron® trademark. Mixtures of xyleneisomers generally contain about 24 weight percent para-xylene in theequilibrium mixture. Para-xylene is usually separated from such mixturesby expensive superfraction and multistage refrigeration steps. Theprocess of this invention affords a xylene product in which para-xylenepredominates. The improved yield of para-xylene, up to a fourfoldincrease over the 24 percent equilibrium concentration, reduces the costof production and separation of para-xylene from the ortho- andmeta-isomers.

The characteristic high yields of para-xylene are believed the resultfrom selectivity of the crystalline silica catalyst to an alkylationmechanism. The alkylation resulting in high para-selectivity is believedto take place inside the pore structure while the crystal surfacereaction sites, which can give rise to undesired side products viaisomerization, disproportionation, alkyl exchange, and reactions ofmethylating agent with itself, are of relatively low activity. The useof promoters further enhances the product contribution from thealkylation occurring inside the pores versus the undesirable surfacereactions. Presence of other metals, e.g., aluminum, as an intrinsicpart of prior art crystalline catalysts is associated with excessivereactivity to form undesired side products. Particularly undesirable isthe reaction of methylating agent to olefins and alkanes therebydecreasing para-xylene yield based on methylating agent.

DETAILS OF THE INVENTION

The process of this invention can be carried out as a batch type,semi-continuous or continuous operation utilizing a fixed or moving bedcatalyst system. Multiple injection of the methylating agent may beemployed. One embodiment entails use of a fluidized catalyst zonewherein the reactants are passed concurrently or countercurrentlythrough a moving fluidized bed of the catalyst. The catalyst, of course,can be regenerated after use.

Toluene and methylating agent are usually premixed and fed together intothe reaction vessel to maintain the desired ratio between them with nolocal concentration of either reactant to disrupt reaction kinetics.Individual feeds can be employed, however, if care is taken to insuregood mixing of the reactant vapors in the reaction vessel. Instantaneousconcentration of methylating agent can be kept low by staged additionsthereof. By staged additions, toluene/methylating agent concentrationscan be maintained at optimum levels to give good toluene conversions.Hydrogen gas can be supplied to the reaction as an anticoking agent anddiluent.

The catalyst and reactants can be heated to reaction temperatureseparately or together. Reaction temperatures are about 400° C. to 650°C., preferably about 500° C. to 600° C., and most preferably about 550°C. Higher temperatures than about 650° C. may cause disproportionation,coking, and dealkylation; lower temperatures than about 400° C., willslow the reaction rate.

Reaction pressures can vary from subatmospheric to superatmospheric.Pressures between about 50 kPa and 4,000 kPa or higher are operable;preferred pressures are 100 kPa to 2,000 kPa. As pressures increase, theamount of ortho- or meta-xylene isomer may increase.

The crystalline silica employed in the process of this invention is madeby heating a reaction mixture containing water, a silica-source, such assilica sols, alkali metal silicates, silica gels, fumed silicas, etc.,and an alkylonium compound, such as quaternary ammonium or phosphoniumsalts, under hydrothermal conditions at a pH of 10 to 14. The pH can becontrolled with alkali metal hydroxide. Heating is continued untilcrystalline silica is formed. Typical reaction temperatures and timesfor crystalline silica formation are 150° to 200° C. for about 30 to 100hours. The product is then separated from the liquid by filtration,washed with water, and dried at 95° to 105° C. for 8 to 16 hours. Thecrystalline silica is characterized by the X-ray powder diffractionpattern shown in Table A.

Crystalline silica obtained by the procedure of the preceding paragraphis catalytically inactive until activated in air or N₂ at about 200° C.to 550° C. for about 4 hours followed by base exchange with ammoniumsalts, such as ammonium nitrate, followed by calcination in air or N₂for several hours at about 200° C. to 550° C. A third heating sequence(thermal activation) at about 200° C. to 550° C. in air or N₂ isnecessary if the activated crystalline silica is treated with a promoteror promoter precursor. This third heating sequence is employed aftersuch treatment and before catalyst use.

As will be appreciated by those skilled in the art, time and temperatureare interrelated so that, within the spirit of the disclosure presentedherein, activation temperatures and other temperatures, may exceed thoseset out if heating times are correspondingly reduced. Likewise, somewhatlower temperatures may be employed if heating times are correspondinglyincreased.

Crystalline silica, preferably in an active form, can be combined withone or more promoters by an appropriate technique selected from one ormore of the following: impregnation, adsorption, physical mixing,chemical reaction, or coating. Reaction of the active crystalline silicawith arsenic-, phosphorus-, magnesium-, boron-, antimony-, andsilicon-containing promoters is effected by contacting the activatedcrystalline silica with any of these compounds in their oxide or oxideprecursor form. Suitable compounds include arsenic (III) butoxide,triethylphosphate, magnesium oxide, boric oxide, trimethylborate,antimony oxide, antimony (III) butoxide, silanes and silicones. Thesilanes and silicones can be used to contact the crystalline silicawhile in the form of liquids, solutes in solution, or gases.

The silanes have the general formula: ##STR1## where n is 1 or 2; R is areactive group such as hydrogen, alkoxy, halogen, carboxy, amino, andacetamide; R₁ can be the same as R; or R₁ can be an alkyl of 1 to about40 carbon atoms; an alkyl or aryl carboxylic acid wherein the alkylgroup contains about 1 to 30 carbon atoms and the aryl group containsabout 6 to 24 carbon atoms; an aryl of about 6 to 24 carbons which maybe further substituted; or an alkaryl or aralkyl containing about 7 to30 carbon atoms. Preferably, the alkyl group of an alkyl silane has from1 to 4 carbon atoms and the carbon chain of an alkoxy group has from 1to 6 carbon atoms. Alkoxy-containing silanes are preferred. One suchpreferred alkoxy-containing silane is tetraethoxysilane(ethylorthosilicate). Mixtures of the above compounds can also be used.

The silicone compounds have the general formula: ##STR2## where R₁ ishydrogen, fluorine, hydroxy, alkyl, aralkyl, alkaryl or fluoro-alkyl.The hydrocarbon substituents generally contain from 1 to 10 carbon atomsand preferably are methyl or ethyl groups. R₂ is selected from the samegroup as R₁, other than hydrogen, and n is an integer of at least 10 andgenerally in the range of 10 to 1000. The molecular weight of thesilicone compound employed is generally between about 500 and 20,000 andpreferably within the approximate range of 1000 to 10,000.Representative silicone compounds include dimethylsilicone,diethylsilicone, phenylmethylsilicone, methylhydrogensilicone,ethylhydrogensilicone, phenylhydrogensilicone, methylethylsilicone,phenylethylsilicone, diphenylsilicone, methyltrifluoropropylsilicone,ethyltrifluoropropylsilicone, polydimethylsilicone,tetrachlorophenylmethyl silicone, tetrachlorophenylethylsilicone,tetrachlorophenylhydrogensilicone, tetrachlorophenylphenylsilicone,methylvinylsilicone and ethylvinylsilicone. Phenylmethylsilicone ispreferred.

The promoter can be in the form of a liquid or solid. A solvent can beemployed to dissolve the promoter, followed by contact with thecrystalline silica. Any solvent which is inert to reaction with thepromoter can be used, including water, alcohols, and aliphatic oraromatic hydrocarbons. The promoter can also be used neat, by soaking oradmixture with the crystalline silica.

The promoter oxides or precursors, used neat or dissolved in a suitablesolvent such as n-hexane, benzene, toluene, xylene, chloroform or carbontetrachloride, are contacted with the activated crystalline silicabetween 25° C., and 100° C. for a period of time sufficient to depositthe desired amount of promoter thereon. The contact time will usuallyvary from 1 to 16 hours. Solvent, if used, is then removed by filtrationor evaporation. The promoted crystalline silica is then dried at 95° to125° C. in nitrogen or air for several hours. Activation of promotedcrystalline silica is achieved by calcination at temperatures up toabout 550° C. Preferably, the calcination temperature is raised slowly,e.g., 1° to 10° C./min until about 550° C. is reached and then held fora time sufficient to complete the activation.

In practicing the alkylation process of this invention, it may bedesirable to incorporate the crystalline silica in another materialresistant to alkylation temperatures and conditions. Such matrixmaterials include synthetic or naturally occurring substances as well asinorganic materials such as clay, silica and metal oxides. The lattermay be either naturally occurring or in the form of gelatinousprecipitates or gels including mixtures of silica and metal oxides.Naturally occurring clays which can be composited with the crystallinesilica include those of the montmorillonite and kaolin families. Thematrix can be in the form of a cogel. The relative proportions of finelydivided crystalline silica and inorganic oxide gel matrix can varywidely with the crystalline silica content ranging from about 1 to 90percent by weight and more usually in the range of about 2 to 70 percentby weight of the composite.

Specific details concerning preparation of several representativecatalysts can be found in Preparations A to L preceding the Examples.

EXAMPLES AND PREPARATIONS

The Examples illustrate the process of this invention. The Preparationspreceding the Examples illustrate several catalysts which are useful inthe process of this invention.

PREPARATION A

Crystalline silica catalyst was prepared from the following reactants:

    ______________________________________                                        (C.sub.2 H.sub.5).sub.4 NBr                                                                         576    g                                                NaOH                  152    g                                                H.sub.2 O             540    g                                                30% SiO.sub.2         6350   g.                                               ______________________________________                                    

The 30% SiO₂ was obtained as Ludox®SM a 30% dispersion of colloidalsilica in water containing small amounts of sodium impurity.

An aqueous solution of (C₂ H₅)₄ NBr and NaOH was mixed vigorously for 15minutes at 35° C. with the colloidal silica. This mixture was charged toa 3 gallon Hastelloy C autoclave and sealed. The temperature of thevessel was raised to 160° C. at 10°/min with slow (75 to 95 RPM)stirring and held for 4 days at 160° C. with slow stirring.

The solid crystalline product was filtered from the slurry and washedwith water to remove unreacted salts and soluble reactants. It was thendried at 95° C. in nitrogen.

X-ray analyses established the material as 100% crystalline silica.Analysis of a dried sample was as follows:

    ______________________________________                                        N          0.70   weight percent                                              C          5.26   weight percent                                              Na.sub.2 O 0.63   weight percent                                              H.sub.2 O  1.2    weight percent                                              SiO.sub.2  92.2   weight percent                                              Al.sub.2 O.sub.3                                                                         508    ppm (about 0.05 weight percent).                            ______________________________________                                    

The crystalline silica was calcined in air at 550° C. for 4 hours andthen exchanged with ammonium by contacting two successive times at 95°C. with 10% NH₄ NO₃ solution (1 gram per 10 grams of crystallinesilica), first for 16 hours, and then for 4 hours. The catalystprecursor was then filtered, washed with H₂ O, dried at 95° C. in N₂,and calcined (activated) in air for 4 hours at 550° C. The surface areaafter activation was 320 m² /g.

PREPARATION B

A catalyst consisting of crystalline silica having an amorphous coatingof silica was prepared in the following manner. Crystalline silica,prepared by the procedure of Preparation A, in the amount of 75 gramswas stirred in a solution of 13.2 grams of ethyl orthosilicate in 880 mlof n-hexane at 25° C. for 2 to 3 hours. The solvent was slowly removedon a rotary evaporator and dried at 95° C. in N₂. The catalyst wasactivated by heating to 500° C. according to this procedure:

25° to 120° C., then 1 hour at that temperature,

120° to 200° C., then 1 hour at that temperature,

200° to 250° C., then 1 hour at that temperature,

250° to 350° C., then 1 hour at that temperature,

350° to 400° C., then 1 hour at that temperature,

400° to 450° C., then 1 hour at that temperature,

450° to 500° C., then 5 hours at that temperature.

The theoretical amount of silica deposited was 5% based on total weightof metal oxides in the catalyst.

PREPARATION C

A catalyst was prepared by stirring 100 grams of crystalline silica,prepared by the procedure of Preparation A, in a solution of 21.5 gramsof boric acid and 250 ml of H₂ O at 80° C. for 16 hours. The mixture wasconcentrated to a paste and dried at 100° C. in N₂. Activation of thecatalyst was preformed by heating it in air at 200° C. for 2 hours, thenat 500° for 16 hours. The concentration of boric oxide on crystallinesilica was 9% based on total weight of metal oxides in the catalyst.

PREPARATION D

Crystalline silica, prepared by the procedure of Preparation A, in theamount of 8.5 grams, was added to a solution of 1.5 grams ofethylorthosilicate in 100 ml of n-hexane. The mixture was stirred for 1hour at 25° C. followed by removal of solvent on a rotary evaporator.The catalyst precursor was dried at 95° C. in nitrogen followed by theslow calcination described in Preparation B except that the activatedcatalyst was kept at 500° C. for 4 hours and not 5 hours. The amount ofsilica deposited was about 5% based on total weight of metal oxides inthe catalyst.

PREPARATION E

Crystalline silica, prepared by the procedure of Preparation A, in theamount of 50 grams was added to a solution of 50 grams of antimony (III)butoxide in 300 ml of dry xylene and refluxed for 16 hours undernitrogen. The cooled mixture was filtered under nitrogen and washed withtoluene, methanol and petroleum ether. The catalyst precursor was airdried at room temperature for two hours and then heated at 95° C. innitrogen for two days. The catalyst was formed into pellets of 3/16 inchand calcined for 4 hours at 500° C.

PREPARATION F

An amount of 133 grams of crystalline silica, prepared by the procedureof Preparation A, was stirred in a solution of 28.6 grams of boric acidand 333 ml of distilled water at 80° C. for 16 hours. The slurry wastransferred to an evaporating dish and concentrated to a paste on a hotplate. The mixture was dried in nitrogen at 100° C. followed by heatingin air at 200° C. for 2 hours and then 500° C. for 16 hours. Thecalcined catalyst contained approximately 10% of B₂ O₃ based on thetotal weight of metal oxides in the catalyst.

PREPARATION G

Crystalline silica was prepared from the following reactants:

    ______________________________________                                        (C.sub.2 H.sub.5).sub.4 NBr                                                                         57.6   g                                                NaOH                  15.2                                                    H.sub.2 O             140    g                                                fumed SiO.sub.2       190    g.                                               ______________________________________                                    

The fumed SiO₂ was obtained as Cab-O-Sil®HS-5.

An aqueous solution of (C₂ H₅)₄ NBr and NaOH (in 55 ml of water) wasadded to a mixture of 190 grams of fumed silica and 855 ml of water withvigorous stirring at 25° C. The mixture was stirred for an additional 15minutes until a homogeneous mix resulted.

The mixture was charged to a 4-liter titanium autoclave and sealed. Thetemperature of the vessel was raised to 160° C. at 10°/min with slowstirring and maintained at 160° C. for 60 hours. The solid crystallineproduct was filtered and washed to remove the soluble salts. The productwas dried in nitrogen at 95° C.

Product analysis of a dried sample was:

    ______________________________________                                        [(C.sub.2 H.sub.5).sub.4 N].sub.2 O                                                          9.62   weight percent                                          H.sub.2 O      1.05   weight percent                                          Na.sub.2 O     0.43   weight percent                                          Al.sub.2 O.sub.3                                                                             365    ppm (about 0.04 weight                                                        percent)                                                SiO.sub.2      88.9   weight percent (by diff).                               ______________________________________                                    

The crystalline silica was calcined in air at 550° C. for 4 hours andexchanged with ammonium by contacting two successive times at 95° C.with 10% NH₄ NO₃ solution, first for 16 hours and then for 4 hours. Theexchanged catalyst was filtered, washed with H₂ O and dried at 95° C. innitrogen. Final activation was performed at 550° C. for 4 hours in air.

PREPARATION H

Crystalline silica, prepared by the procedure of Preparation A, in theamount of 20 g, was added to a solution of 2.5 grams of a phenylmethyldiphenyl silicone (MW 8000) in 200 ml of n-hexane. The mixture wasstirred for 16 hours at 25° C. followed by removal of solvent on arotary evaporator. The catalyst precursor was dried at 95° C. innitrogen followed by the slow calcination described in Preparation B.

PREPARATION I

Crystalline silica, prepared by the procedure of Preparation A, in theamount of 42.5 g, was added to a solution of 7.5 g of ethylorthosilicatein 500 ml of n-hexane. The mixture was stirred for 1 hour at 25° C.followed by removal of solvent on a rotary evaporator. The catalystprecursor was dried at 95° C. in N₂ followed by the slow calcinationdescribed in Preparation B. The calcined catalyst was mixed with asecond solution of 7.5 g of ethylorthosilicate in 500 ml of n-hexane for2 hours at 25° C. The catalyst precursor, after removal of solvent anddrying in N₂ at 95° C., was activated a second time employing a slowcalcination in air at 25° C. to 525° C. at incremental increases of2°/min, then at 525° C. for 4 hours.

The activated catalyst was mixed with montmorillonite clay and water(60% crystalline silica, 40% montmorillonite binder on ignited basis)and then extruded to form 1/16 inch pellets. The pellets were dried at95° C. in N₂ for 8 hours to use.

PREPARATION J

Crystalline silica, prepared by the procedure of Preparation A, in theamount of 9 g was stirred in a solution of 2.0 g of phenylmethylsilicone(MW 4000) in 100 ml of n-hexane at 25° C. for 1 hour. The solvent wasremoved on a rotary evaporator. The catalyst precursor was thenactivated in air at 25° C. to 540° C. at incremental increases of1°/min, then at 540° C. for 7 hours.

PREPARATION K

Crystalline silica, prepared by the procedure of Preparation A, wasadded to a solution of ethylorthosilicate in 100 ml of n-hexane. Theweights of crystalline silica and ethylorthosilicate were varied toyield a deposition weight of SiO₂ ranging from 0.5 to 18 weight percent.The weight of crystalline silica to volume of hexane ranged from 0.08 to0.10. The mixture was stirred for 1 hour at 25° C. followed by removalof solvent on a rotary evaporator. Each sample of coated catalyst wasthen activated by heating to 550° C. at 10°/min followed by heating for7 hours in air at 550° C.

PREPARATION L

Crystalline silica, prepared by the procedure of Preparation A, wasadded to a solution of ethylorthosilicate in 100 ml of n-hexane. Theweights of crystalline silica and ethylorthosilicate were varied toyield a deposition weight of SiO₂ ranging from 0.3 to 5 weight percent.The weight of crystalline silica to volume of hexane ranged from 0.085to 0.099. The mixture was stirred for 1 hour at 25° followed by removalof solvent on a rotary evaporator. The catalysts were then dried at 95°C. in N₂ for 16 hours followed by activation as described in PreparationB.

EXAMPLES 1 TO 3

An amount of 3.6 g of the catalyst of Preparation A was placed in a 1inch diameter quartz reactor inserted in a split-tube furnace andemployed in three successive methylations of toluene to paraxylene. A3/1 mole ratio of toluene to methanol together with a concurrenthydrogen (H₂) feed, in a ratio of H₂ to hydrocarbon (HC) of 0.8, waspassed over the powder catalyst at 101 kPa (1 atm.). The reactionconditions and results expressed in mole percent are summarized in Table1.

                  TABLE 1                                                         ______________________________________                                                     Weight                    Per-                                        Tol-    Hourly         Mole Percent                                                                             cent Para                              Ex.  uene/   Space    Temp. Conversion Selectivity                            No.  MeOH    Velocity °C.                                                                          Toluene                                                                              MeOH  In Xylene                            ______________________________________                                        1    3       3.9      450   14.6   88    56                                   2    3       3.9      500   19.6   95    53                                   3    3       3.9      550   26.3   95    51                                   ______________________________________                                    

EXAMPLES 4 TO 9

An amount of 3.6 grams of the catalyst of Preparation D was charged to a1 inch diameter quartz reactor and employed in six successive catalyticmethylations of toluene at 101 kPa. A solution of toluene and methanolalong with a feed of H₂ (H₂ /HC=0.8) was passed over the catalyst underthe conditions and with the results summarized in Table 2.

                  TABLE 2                                                         ______________________________________                                                     Weight                    Per-                                        Tol-    Hourly         Mole Percent                                                                             cent Para                              Ex.  uene/   Space    Temp. Conversion Selectivity                            No.  MeOH    Velocity °C.                                                                          Toluene                                                                              MeOH  In Xylene                            ______________________________________                                        4    3       3.9      450   13.4   99    94                                   5    3       3.9      500   16.6   99    93                                   6    3       3.9      550   18.8   99    93                                   7    3       3.9      600   20.1   99    92                                   8    10      3.9      500   8.4    99    93                                   9    10      3.9      550   9.6    99    91                                   ______________________________________                                    

EXAMPLES 10 TO 12

An amount of 3.6 grams of the catalyst of Preparation E was charged to a1 inch diameter quartz reactor and employed in three successive toluenemethylations. A 3/1 mole ratio of toluene to methanol together with afeed of H₂ (H₂ /HC=0.8) was passed over the catalyst pellets at 101 kPaunder the reaction conditions and with the results summarized in Table3.

                  TABLE 3                                                         ______________________________________                                                     Weight                    Per-                                        Tol-    Hourly         Mole Percent                                                                             cent Para                              Ex.  uene/   Space    Temp. Conversion Selectivity                            No.  MeOH    Velocity °C.                                                                          Toluene                                                                              MeOH  In Xylene                            ______________________________________                                        10   3       4.4      450   8.6    90    72                                   11   3       4.4      500   14.9   90    72                                   12   3       4.4      550   19.3   90    75                                   ______________________________________                                    

EXAMPLES 13 TO 23

Amounts of the catalyst of Preparation F were placed in a 1 inchdiameter quartz reactor and employed at 101 kPa under the reactionconditions and with the results summarized in Table 4. Ananticoking/diluent feed of H₂ (H₂ /HC=0.8) was also employed.

                  TABLE 4                                                         ______________________________________                                                     Weight                    Per-                                        Tol-    Hourly         Mole Percent                                                                             cent Para                              Ex.  uene/   Space    Temp. Conversion Selectivity                            No.  MeOH    Velocity °C.                                                                          Toluene                                                                              MeOH  In Xylene                            ______________________________________                                        13.sup.1                                                                           3       2.5      450   14.7   99    82                                   14.sup.1                                                                           3       2.5      500   18.6   99    82                                   15.sup.1                                                                           3       2.5      550   20.9   99    81                                   16.sup.2                                                                           3       3.9      500   18.1   99    82                                   17.sup.3                                                                           3       9.4      550   21.5   88    75                                   18.sup.2                                                                           5       3.9      500   12.2   94    87                                   19.sup.4                                                                           3       1.0      550   18.1   99    88                                   20.sup.2                                                                           10      3.9      550   8.7    99    90                                   21.sup.5                                                                           3       3.9      500   7.7    70    97                                   22.sup.5                                                                           3       3.9      550   9.5    77    99                                   23.sup.5                                                                           3       3.9      600   8.3    80    98                                   ______________________________________                                         .sup.1 The number of grams of catalyst was 5.7.                               .sup.2 The number of grams of catalyst was 3.6.                               .sup.3 The number of grams of catalyst was 1.5.                               .sup.4 The number of grams of catalyst was 13.5.                              .sup.5 The catalyst, 3.6 grams, was steamed at 550°  C., for 3         hours under 3% H.sub.2 O in nitrogen.                                    

EXAMPLES 24 TO 28

Catalysts prepared by the process of Preparation K were tested for themethylation of toluene along with a H₂ feed (H₂ /HC=0.8) at 101 kPa. Theresults and reaction conditions are summarized in Table 5.

                  TABLE 5                                                         ______________________________________                                             SiO.sub.2                                                                              Weight                                                               Coating  Hourly   Mole Percent                                                                              Percent Para                               Ex.  Weight   Space    Conversion  Selectivity                                No.  Percent  Velocity Toluene MeOH  In Xylene                                ______________________________________                                        24   0.5      5.4      9.4     99    75                                       25   1.0      5.6      9.1     99    70                                       26   5.0      5.4      8.4     99    86                                       27   10.0     6.4      8.2     99    93                                       28   18.0     7.4      8.0     99    94                                       ______________________________________                                    

EXAMPLES 29 TO 32

An amount of 3.6 g of the catalyst of Preparation A was charged to a 1inch diameter quartz reactor and tested for the methylation of tolueneemploying a 10/1 toluene/methanol feed along with a hydrogen feed (H₂/HC=0.8) at 101 kPa pressure.

                  TABLE 6                                                         ______________________________________                                                       Weight                                                                        Hourly   Mole Percent                                                                              Percent Para                              Ex.  Temp.     Space    Conversion  Selectivity                               No.  °C.                                                                              Velocity Toluene MeOH  In Xylene                               ______________________________________                                        29   500       3.9      8.2     99    43                                      30   550       3.9      9.1     99    47                                      31   550       7.8      8.3     95    66                                      32   550       15.6     6.5     77    72                                      ______________________________________                                    

EXAMPLES 33 TO 40

An amount of 3.6 g of the catalyst of Preparation H was charged to a 1inch diameter quartz reactor and tested in toluene methylation employinga concurrent H₂ feed. The reaction conditions and results are summarizedin Table 7.

                                      TABLE 7                                     __________________________________________________________________________     No.Ex.                                                                           VelocitySpaceHourlyWeight                                                          °C.Temp.                                                                   ##STR3##                                                                          ##STR4##                                                                            TolueneMeOHConversionMole Percent                                                     In XyleneSelectivityPercent                    __________________________________________________________________________                                  Para                                            33  3.9 550 0.8  3    19.2                                                                               99   84                                            34  3.9 600 0.8  3    20.0                                                                               99   84                                            35  3.9 500 0.8 20     5.0                                                                               99   81                                            36  3.9 550 0.8 20     5.6                                                                               99   81                                            37  3.9 500 0.8 10     8.3                                                                               99   84                                            38  3.9 550 0.8 10     9.4                                                                               99   84                                            39  7.8 550 0.4 10     8.4                                                                               99   83                                            40 15.6 550 0.2 10     7.9                                                                               99   92                                            __________________________________________________________________________

EXAMPLES 41 TO 44

An amount of 3.6 g of the catalyst of Preparation D was charged to a 1inch diameter quartz reactor and employed in four successive toluenemethylations at 101 kPa pressure employing a 3/1, toluene/methanol, moleratio. A concurrent feed of H₂ (H₂ /HC=0.8) was employed.

                  TABLE 8                                                         ______________________________________                                             Weight                                                                        Hourly            Mole Percent                                                                              Percent Para                               Ex.  Space     Temp.   Conversion  Selectivity                                No.  Velocity  °C.                                                                            Toluene MeOH  In Xylene                                ______________________________________                                        41   3.9       450     13.4    99    94                                       42   3.9       500     16.6    99    93                                       43   3.9       550     19.7    99    93                                       44   3.9       600     20.1    99    92                                       ______________________________________                                    

EXAMPLES 45 TO 47

An amount of 3.6 g of 1/16 inch extrudate catalyst of Preparation I wascharged to a 1 inch diameter quartz reactor and tested for itsmethylation activity with toluene. A feed of 10/1, toluene/methanol,along with a concurrent feed of hydrogen (H₂ /HC=0.8) was employed at aspace velocity of 3.9 hr⁻¹ and 101 kPa pressure. The reaction conditionsand results are summarized in Table 9.

                  TABLE 9                                                         ______________________________________                                                        Mole Percent    Percent Para                                  Ex.     Temp.   Conversion      Selectivity                                   No.     °C.                                                                            Toluene    Methanol                                                                             In Xylene                                   ______________________________________                                        45      450     5.8        99     89                                          46      500     7.5        99     90                                          47      550     8.1        99     89                                          ______________________________________                                    

EXAMPLES 48 TO 50

An amount of 2.5 g of the catalyst of Preparation J was charged to aquartz microreactor and tested for its ability to alkylate tolueneemploying dimethylether (Me₂ O) as the methylating agent. A 5.4/1 moleratio of toluene to dimethylether along with a concurrent feed of H₂ (H₂/toluene of 0.8) was passed over the catalyst at 101 kPa pressure and aspace velocity of 5.3 hr⁻¹ based on toluene fed. The results andreaction conditions are summarized in Table 10.

                  TABLE 10                                                        ______________________________________                                                        Mole Percent   Percent Para                                   Ex.     Temp.   Conversion     Selectivity                                    No.     °C.                                                                            Toluene    Me.sub.2 O                                                                          In Xylene                                    ______________________________________                                        48      450     19.1       80    88                                           49      500     18.0       91    87                                           50      550     21.0       93    88                                           ______________________________________                                    

EXAMPLES 51 TO 53

An amount of 3.6 g of the catalyst of Preparation G was charged to a 1inch diameter quartz reactor and tested for the methylation of tolueneemploying a 10/1 mole ratio of toluene/methanol feed along with ahydrogen feed (H₂ /HC=0.8) at 101 kPa. The reaction conditions andresults are summarized in Table 11.

                  TABLE 11                                                        ______________________________________                                                    Mole Percent   Percent Para                                       Temp.       Conversion     Selectivity                                        Ex. No. °C.                                                                            Toluene    MeOH  In Xylene                                    ______________________________________                                        51      450     4.9        80    80                                           52      500     6.2        84    75                                           53      550     7.1        87    70                                           ______________________________________                                    

EXAMPLES 54 TO 59

An amount of 3.6 g of the silica promoted crystalline silica fromPreparation L was tested for its ability to catalyze the methylation oftoluene at 500° to 550° C. employing toluene and methanol along with afeed of hydrogen (H₂ /HC=0.8). The weight hourly space velocity was 3.9hr⁻¹. The results and reaction conditions are shown in Table 12.

                  TABLE 12                                                        ______________________________________                                         No.Ex.                                                                             PercentWeightCoatingSiO.sub.2                                                          ##STR5##                                                                               °C.Temp.                                                                      eneMeOHTolu-ConversionMole                                                             In XyleneSelectivityParaPercent       ______________________________________                                        54    0.3      3        500   17.1  99     89                                 55    0.3      3        500   21.0  99     86                                 56    1.5     10        500    8.4  98     83                                 57    1.5     10        550    9.4  98     81                                 58    5.0     10        500    8.4  99     93                                 59    5.0     10        550    9.6  99     91                                 ______________________________________                                    

I claim:
 1. In a process for preparing paraxylene by the catalyticreaction of toluene and a methylating agent, the improvement whichcomprises employing a catalyst of crystalline silica and, as promotertherefor, a member of the group consisting of arsenic oxide, magnesiumoxide, boron oxide, antimony oxide, amorphous silica, and mixturesthereof, said promoter being present at 0 to about 50% based on totalweight of metal oxide in the catalyst.
 2. A process according to claim1, employing substantially 0% promoter.
 3. A process according to claim1, employing 0.3% to 25% promoter.
 4. A process according to claim 1,employing as promoter a member of the group consisting of boron oxide,antimony oxide and amorphous silica.
 5. A process according to claim 3wherein the methylating agent is selected from the group consisting ofmethanol and dimethylether.
 6. A process according to claim 4 whereinthe promoter is boron oxide.
 7. A process according to claim 4 whereinthe promoter is antimony oxide.
 8. A process according to claim 4wherein the promoter is amorphous silica.
 9. A process according toclaim 1 wherein the mole ratio of toluene to methylating agent is about1 to 50/1 and the weight of reactant feed per weight of catalyst perhour is about 1 to 500/1.
 10. A process according to claim 5 wherein themole ratio of toluene to methylating agent is about 1 to 50/1 and theweight of reactant feed per weight of catalyst per hour is about 1 to500/1.
 11. A process according to claim 9, employing as promoter amember of the group consisting of boron oxide, antimony oxide andamorphous silica.
 12. A process according to claim 10 employing aspromoter a member of the group consisting of boron oxide, antimony oxideand amorphous silica.
 13. A process according to claim 12 wherein thepromoter is boron oxide.
 14. A process according to claim 12 wherein thepromoter is antimony oxide.
 15. A process according to claim 12 whereinthe promoter is amorphous silica.
 16. A process according to claim 12wherein the methylating agent is dimethylether.
 17. A process accordingto claim 12 wherein the methylating agent is methanol.
 18. A processaccording to claim 17 wherein the mole ratio of toluene to methanol isabout 5 to 15/1 and the weight of reactant feed per weight of catalystper hour is about 3 to 100/1.
 19. A process according to claim 18wherein the promoter is amorphous silica.